Wattmeter
![Wattmeter](/Images/godic/202502/20/Wattmeter1745.jpg")
![Early wattmeter on display at the Historic Archive and Museum of Mining in Pachuca, Mexico](/Images/godic/202502/20/WattmeterAcostaMexico1745.JPG")
![Siemens electrodynamometer, circa 1910,
F = Fixed coil, D = Movable coil, S = Spiral spring, T = Torsion head, M = Mercury cups, I = Index needle](/Images/godic/202502/20/Siemens_electrodynamometer1745.png")
![Prodigit Model 2000MU (UK version), shown in use and displaying a reading of 10 watts being consumed by the appliance](/Images/godic/202502/20/Plug-in_Power_&_Energy_Monitor_in_UK_Domestic_Mains_Socket1745.jpeg")
The wattmeter is an instrument for measuring the electric power (or the supply rate of electrical energy) in watts of any given circuit. Electromagnetic wattmeters are used for measurement of utility frequency and audio frequency power; other types are required for radio frequency measurements.